1. Field of the Invention
The present invention concerns the fields of molecular medicine and targeted delivery of therapeutic agents. More specifically, the present invention relates to the identification of aminopeptidase A (APA) as a therapeutic target in angiogenic blood vessels, and the present invention provides methods and compositions relating to targeting aminopeptidase A for the treatment of cancer
2. Description of Related Art
Phage display or biopanning is a technique which can be used to identify specific peptide sequences that can bind to a target molecule, cell, tissue, or organ. Phage display is a technique in which a phage library expresses, for example, a set of random peptide sequences of defined length, incorporated into a phage coat protein (e.g., Smith and Scott, 1985; Smith and Scott, 1993). Peptide sequences that bind to a target molecule, cell, tissue or organ may be identified by incubating a phage display library with the target and selecting for bound peptides (biopanning) (e.g., Pasqualini and Ruoslahti, 1996; Arap et al., 1998a). Unbound phage may be washed away and bound phage eluted and collected. The collected phage may be amplified and taken through further binding/amplification cycles to enrich the pool of peptides for those that selectively and/or specifically bind to the target. With each cycle, the proportion of phage in the pool that contain targeting peptides for the target of interest is enriched. After several cycles, individual phage clones may be characterized by DNA sequencing to identify the targeting peptide sequences.
Biopanning may be used to select or identify peptides that can be used in developing new therapies or therapeutic compositions or enhancing exisiting therapies. For instance, cancer continues to be a serious problem in society, resulting in significant mortality rates. The realization that angiogenic vasculature is a target for intervention in cancer has long led to an interest in endothelial cell receptors associated with tumor blood vessels and their corresponding ligands. However, so far only a few such receptors have been identified. Even less is known about the function and physiologic significance of these receptors, which include aminopeptidase A.
Aminopeptidase A (glutamyl-aminopeptidase, EC 3.4.11.7, APA) is a homodimeric type II membrane-spanning cell surface protein with zinc metallopeptidase activity that hydrolyzes N-terminal glutamyl or aspartyl residues from oligopeptide substrates (Nanus et al., 1993; Wu et al., 1990). Upregulation of APA has been reported in perivascular cells (termed “pericytes”) of tumor blood vessels (Alliot et al., 1999a; Schlingemann et al., 1996; Juillerat-Jeanneret et al., 2003; Juillerat-Jeanneret et al., 2000; Bogenreider et al., 1997; Alliot et al., 1999b); however, no role or physiologic function has been established for APA in tumor blood vessels.
Targeting peptides that exhibit selective and/or specific binding for aminopeptidase A have not been previously reported in the literature. Further characterization of APA is needed.